The present invention relates to a wafer having a laser mark for indication of a crystal orientation, specification, etc.
A wafer sliced off an ingot is processed in various steps such as lapping, chamfering and etching. In these steps, a mark for indication of a crystal orientation is carved on an edge of the wafer. The mark is used for setting the wafer, when the wafer is scribed along a cleavage plane for instance.
Such a mark has been put on a wafer by various methods.
The method is the most popular one by which an orientation flat is formed at an edge of a wafer. The orientation flat is used for a crystal orientation of the wafer in later steps. However, it is difficult to precisely align a wafer using the orientation, since the orientation flat is formed in a relatively broad area crossing an edge of the wafer at an obtuse angle. The orientation flat also reduces an effective area of the wafer. Besides, the orientation flat puts restrictions on a shape of an electrostatic chuck which is used for handling a wafer and causes a harmful effect on dynamic balance during spin rotation of a wafer.
A notch engraved on an edge of a wafer is also used as a mark or indication of a crystal orientation. In this case, a notched edge is polished to specular glossiness, so as to distinctly detect the notched part during measuring in later steps. Such polishing is troublesome, and residual stresses inevitably remain near the notched part. It is difficult to completely remove such residual stresses.
A laser mark useful an indication of a crystal orientation has been recently proposed. The laser mark is put on a front or back side of a wafer by partially melting a surface layer of the wafer with irradiation of a laser beam. The laser mark can be easily carved on the front or back side of the wafer without introduction of any mechanical stresses. However, the laser mark reduces an effective area of a wafer, and inevitably requires a troublesome process for rectifying data so as to eliminate errors caused by the marked part during measuring a shape of the wafer.